instant death
Yeah, no. Instant-deaths are pretty damn stupid, and especially so in a Musou-type game. Things like that should work in the way
LoS handled it. You're sent back a little bit, but you lose a chunk of health. Or even they could deliver quite a bit of damage, and then throw you aside.
Bottomless pits should be handled the same way. When it's REALLY easy to misjudge a jump, bottomless pits shouldn't be an instant death. If they did, it's more of a frustrating challenge rather than just being... well, challenging.
The status effects are good ideas, but they should only reduce health to 1, so you actually have a chance should you not be around healing items (since if this would be anything like an actual Musou game, health items would be scarce). One differing thing VAMP could do besides just gradually taking health away is to also affect how you perform in battle. For example, you could attack slower as a result of your body being damaged. And then, it could even do the opposite in night-time stages, and instead you attack faster, or your attacks are stronger.
As for story, even an "eh" crossover story would be better than no story at all. Stories help create a goal in a player's mind. Hell, a crossover story could be good if, for once, the story writers start writing the characters in with the mindset of them being in the same time/world to begin with, rather than there being a rip in the time/space continuum or some bullshit that pulls them all into the same era/world.
Co-op is a must in Musou games (I was livid that
Warriors: Legends of Troy didn't have co-op). Co-op should also be both local and online.
But yeah, like said twice already. Konami wouldn't be up to it. Which is a shame, since these crossovers (Musou with another franchise) always bring in some pretty cool ideas. Like
Ken's Rage's skill tree, or
Gundam Musou's ranged combat. Oh well. Tecmo Koei said they're interested in doing more crossovers with Nintendo, so let's hope after
Hyrule Warriors, they do a game for
Fire Emblem.
I think it's more that the good games in the series have been in 2D. If we had a 3D entry in the series that was the true personification of Castlevania in 3D people would be OK with it. It's not that it can't be done, it's that it hasn't been done yet despite many attempts which has soured fans to the prospect of a 3D Castlevania game.
Castlevania 64 could have potentially been this, if they didn't rush it out, and then rush the "sequel". If they spent more time refining the controls and gameplay, it coulda been wonderful.